As one of conventional rotary compressors including a compression mechanism in which a piston (an eccentric rotation body) rotates eccentrically within a cylinder chamber, there has been proposed a rotary compressor in which refrigerant is compressed by volume change of the cylinder chamber in association with eccentric rotation of an annular piston (for example, see Japanese Patent Publication No. 6-288358).
In the compressor (100), a hermetic casing (110) accommodates a compression mechanism (120) and a drive mechanism (an electric motor) (not shown) for driving the compression mechanism (20), as shown in FIG. 12 and FIG. 13 (a section taken along the line XIII-XIII in FIG. 12).
The compression mechanism (120) includes a cylinder (121) having an annular cylinder chamber (C1, C2) and an annular piston (122) arranged in the cylinder chamber (C1, C2). The cylinder (121) includes an outer cylinder (124) and the inner cylinder (125) which are arranged coaxially so that the cylinder chamber (C1, C2) is formed between the outer cylinder (124) and the inner cylinder (125). The outer cylinder (124) and the inner cylinder (125) are integrated by means of a cylinder side end plate (126A) provided at the top end faces thereof.
The annular piston (122) is connected to an eccentric portion (133a) of a drive shaft (133) connected to the electric motor through a piston base (piston side end plate) (126B) in substantially a circular shape so as to rotate eccentrically away from the center of the drive shaft (133). The annular piston (122) eccentrically rotates while being substantially in contact at one point of the outer peripheral face thereof with the inner peripheral face of the outer cylinder (124) (wherein, “substantially in contact” means a state in which though a minute gap is present to an extent that an oil film is formed, leakage of refrigerant in the gap is ignorable) and keeping substantially in contact at one point of the inner peripheral face 180° different in phase from the contact point with the outer peripheral face of the inner cylinder (125). Thus, an outer cylinder chamber (C1) and an inner cylinder chamber (C2) are formed on the outside and the inside of the annular piston (122), respectively.
An outer blade (123A) is arranged outside the annular piston (22). The outer blade (123A) is forced inward in the radial direction of the annular piston (122) so that the inner peripheral end thereof pushes and is in contact with the outer peripheral face of the annular piston (122). The outer blade (123A) divides the outer cylinder chamber (C1) into a high pressure chamber (a first chamber) (C1-Hp) and a low pressure chamber (a second chamber) (C1-Lp).
On the other hand, an inner blade (123B) is arranged inside the annular piston (123) on an extension line of the outer blade (123A). The inner blade (123B) is forced outward in the radial direction of the annular piston (122) so that the outer peripheral end thereof pushes and is in contact with the inner peripheral face of the annular piston (122). The inner blade (123B) divides the inner cylinder chamber (C2) into a high pressure chamber (a first chamber) (C2-Hp) and a low pressure chamber (a second chamber) (C2-Lp).
Further, in the outer cylinder (124), an intake port (141) for allowing the outer cylinder chamber (C1) to communicate with an intake pipe (114) provided at a casing (110) is formed in the vicinity of the outer blade (123A). Also, in the annular piston (122), a through hole (143) is formed in the vicinity of the intake port (141) so that the low pressure chamber (C1-Lp) of the outer cylinder chamber (C1) and the low pressure chamber (C2-Lp) of the inner cylinder chamber (C2) communicate with each other through the through hole (143). Further, a discharge port (not shown) for allowing the high pressure chambers (C1-Hp, C2-Hp) of the cylinder chambers (C1, C2) to communicate with a high pressure space (S) in the casing (110) is formed in the compression mechanism (120).
In the thus constructed compressor (100), when the drive shaft (133) rotates to eccentrically rotate the annular piston (122), volume expansion and contraction are repeated alternately in both the outer cylinder chamber (C1) and the inner cylinder chamber (C2). In the volume expansion of the respective cylinder chambers (C1, C2), a sucking process is performed in which the refrigerant is sucked into the respective cylinder chambers (C1, C2) from the intake port (141). While in the volume contraction, a compression process in which the refrigerant is compressed in the respective cylinder chambers (C1, C2) and a discharge process in which the refrigerant is discharged from the respective cylinder chambers (C1, C2) to the high pressure space (S) in the casing (110) through the discharge port are performed. Thus, the refrigerant at high pressure discharged in the high pressure space (S) of the casing (110) flows into a condenser of a refrigeration circuit through a discharge pipe (115) provided in the casing (110).
In the compressor (100) in this case, a support plate (117) for supporting the piston side end plate (126B) is formed at the lower face of the end plate (126B) connected to the annular piston (122). A sealing ring (129) is provided coaxially with the annular piston (122) at a part where the piston side end plate (126B) faces the support plate (117). The piston side end plate (126B) receives at a part thereof corresponding to the inner peripheral side of the sealing ring (129) pressure of the refrigerant in the high pressure space (S). This causes the piston side end plate (126B) to push upward in the axial direction towards the cylinder (121) to minimize gaps in the axial direction between the cylinder (121) and the annular piston (123) (a first axial-direction gap between the lower end face in the axial direction of the cylinder (121) and the piston side end plate (126B) and a second axial-direction gap between the upper end face in the axial direction of the piston (122) and the cylinder side end plate (126A)).
In the conventional construction as shown in FIG. 12 and FIG. 13, when pressure in the cylinder chambers (C1, C2) become high in the compression process, for example, gas force (a downward thrust load) in the axial direction is liable to work on the piston side end plate (126B) formed at the lower end of the annular piston (122). If the thrust load would become large or a point of action of the thrust load would be away from the axial center of the drive shaft (133), the piston side end plate (126B) and the annular piston (122) fixed to the end plate (126B) may incline (be turned over) with respect to the drive shaft (133) when a moment (a turnover moment) working on the piston side end plate (126B) exceeds a predetermined value. When a gap is generated between the annular piston (122) and the cylinder (121) by such turnover of the annular piston (122), the refrigerant leaks through the gap to lower the compression efficiency.
In the above conventional construction, the turnover moment caused due to the thrust load might be mitigated in such a manner that pressing force in the axial direction, which is obtained from the pressure at the part of the piston side end plate (126B) corresponding to the inner peripheral side of the sealing ring (129), works on the piston side end plate (126B) against the thrust load. However, the mitigation is insufficient because of the following reasons.
FIG. 14 is an explanatory drawing showing step by step eccentric motion of the annular piston (122) in the conventional construction. By driving the drive shaft (133), the annular piston (122) eccentrically rotates within the cylinder chamber (C1, C2) in the order shown in FIG. 14(A) to FIG. 14(D). When the annular piston (122) is in the state shown in FIG. 14(A), the pressure of the refrigerant in the high pressure chamber (C2-Hp) of the inner cylinder chamber (C2) rises to allow the center of the thrust load (PT) to move on the upper face of the piston side end plate (126B) towards the high pressure chamber (C2-Hp) in the radial direction, as shown by the arrow (PT) in FIG. 14. In contrast to the thrust load (PT), the pressing force (the arrow (P) in FIG. 14) obtained from the sealing ring (129) is centered on the center of the sealing ring (129) on the lower face of the piston side end plate (126B), in other words, on the center of the annular piston (122). This means that the point of action of the axial-direction pressing force (P) is different in the radial direction from the point of action of the thrust load (PT) working on the piston side end plate (126B), causing difficulty in effective mitigation of the turnover moment.
Further, in the state shown in FIG. 14(B) in which the inner pressure of the high pressure chamber (C2-Hp) of the inner cylinder chamber (C2) becomes high and the inner pressure of the high pressure chamber (C1-Hp) of the outer cylinder chamber (C1) becomes slightly high, the thrust load (PT) works on a part near the high pressure chambers (C1-Hp, C2-Hp) while the axial-direction pressing force (P) obtained from the sealing ring (129) works on a part near the low pressure chamber (C2-Lp), which is the center of the annular piston (122). Accordingly, the point of action of the axial-direction pressing force (P) further separates from the point of action of the thrust load (PT), inviting further difficulty in mitigation of the turnover moment.
In addition, in the state shown in FIG. 14(D) in which the inner pressure of the high pressure chamber (C1-Hp) of the outer cylinder chamber (C1) becomes high and the inner pressure of the high pressure chamber (C2-Hp) of the inner cylinder (C2) becomes slightly high, the thrust load (PT) is centered at a part near the high pressure chambers (C1-Hp, C2-Hp), resulting in separation of the point of action of the axial-direction pressing force (P) from the point of action of the thrust load (PT) to invite difficulty in effective mitigation of the turnover moment, as well.
As described above, in the conventional construction, the axial-direction pressing force (P) obtained from the sealing ring (129) hardly agrees with the thrust load (PT) in eccentric rotation of the annular piston (122), attaining ineffective restraint on turnover of the annular piston (122).
The present invention has been made in view of the above problems and has its objective of restraining turnover of an eccentric rotation body such as an annular piston by effectively exerting axial-direction force against a thrust load working on a end plate of the eccentric rotation body.